1. Field of the Invention
The present invention refers to a helical, flexible, sound-absorbing tube including a non-porous, variable-width film interposed between porous helical tapes that form the walls of the tube such as to regulate the porosity of the tube.
2. Description of Related Art
Those skilled in the art are aware that the acoustic attenuation phenomenon in a a tube is due to absorption by the porous walls of the tube of the sound waves propagated by air condition inside the tube. The walls of the tube acts as a trap that capture and transform the sound waves into heat.
Accordingly, by controlling the tube wall porosity one can control the acoustical attenuation.
Currently, flexible tubes for conducting air are employed in several industries, such as the automotive industry. The tubes are manufactured by braiding or weaving threads over metallic or non-metallic supports. These flexible tubes, by reason of their construction, prevent the excessive propagation of mechanical noises. However, the process used to manufacture such flexible tubes is relatively slow and, accordingly, of a relatively high cost, resulting from the manufacturer having to deal with several product treatments in order to obtain the desired construction. There is also a similar manufacturing process employing the overlaying and gluing of porous strips over a helical support of metallic or non-metallic wire. The sound-absorption qualities of said tubes are obtained by spraying a varnish or the like over the tubes, that externally and partially obstructs the porosity attained in the construction of those tubes.
Also in the current international technology there are flexible, air-conducting tubes manufactured by the helical overlaying of uniform strips, wave-shaped or not, made of several materials, that can be glued or heat-adhered to each other, noting that said uniform strips are made of metallic material, plastic material of composite fibrous material and that the manufacturing process for these flexible tubes is quick, the strength and hermetical features of each flexible tube taking place by the helical overlay of the uniform strips. However, this type of tube tends to allow the excessive propagation of mechanical noises. Some of those tubes employ porous strips of cotton textile or the like, non-woven textile, such as non woven polyester textile or filter porous paper, noting that said porous strips are glued over a perforated metallic or non-metallic strip that serves as a support, thereby causing an acoustic attenuation effect. The acoustic control is determined by the size of the perforations on said support and also by the composition of the porous strips.
All tubes constructed as described above have the drawback of an acoustic control of difficult industrial application, since that, in respect of the first mentioned tubes, the uniform application of the varnish or the like is difficult to control and, in respect of the latter tubes, the exact dimensioning of the perforations on the support is very difficult to obtain, because the tools making such perforations must be constantly redimensioned and changed, depending on the desired sound-absorption effect.
The device for controlling the porosity of an air-conducting, helical flexible sound absorbing tube subject matter of the present patent has been designed to solve the inconveniences and drawbacks described on the report on the state of the art; accordingly, the proposed device is a variable-width, non-porous film which, by means of its helical and discontinued arrangement interposed between the porous layers along a tube allows the accurate control of the porous strips on the wall of said tube, thereby permitting an exact repeatability of the sound absorbing characteristics in the manufacture of the tube and also providing a great ease in the serial manufacture of the tube. Therefore, the scope of this patent complies with the aspects of novelty, inventive activity and industrial application. It should be noted that the proposed device, by reason of its own or aggregated characteristics, allows the industrial manufacture of the pipe, by means of the helical gluing of the porous strips to each other.